Slur Lines don´t get correctly organized

1) Write on the piano a melody on F cleff that goes higher than the G cleff
2) Select the notes which are higher and transport them to the G cleff by using Ctrl+shift+up
3) Put a slur line from the first note on the f cleff to the last note on the G cleff
4) Try to move it so the extremes of the line show the extreme notes slured
5) The program will automatically move the line on a not desired way and change the space between the two systems of the piano instead of organizing the line as you want.